1. Field of the Invention
The present invention relates to a vibration gyro and oscillator available for the detection of a rotational angular velocity, and more particularly to a vibration gyro and oscillator used for position control and vehicle control.
2. Description of the Related Art
Prior vibration gyros are roughly classified into tuning fork types and vibrating reed types in accordance with configurations of oscillators. Of these vibration gyros, the tuning fork type features a high stability of its oscillator and has given satisfactory results in the field of position control and vehicle control which require a high reliability.
As such a tuning fork type vibration gyro, the so-called Watson type have been disclosed in Japanese Unexamined Patent publication Nos. 58-174854, 60-111110, 60-216210, 62-229024 and others. FIG. 13 shows an example of the Watson type vibration gyro. In the Watson type vibration gyro, as shown in FIG. 13 an oscillator 1 comprises two driving tuning fork arm sections 2a, 2b, two detection tuning fork arm sections 3a, 3b respectively connected to one end portions of the driving tuning fork arm sections 2a, 2b, a connecting section 4 for connection between the other end portions of the driving tuning fork arm sections 2a, 2b, a supporting pin 5 for supporting the connecting section 4, and a base 6 for fixing the supporting pin 5. In this case, the driving tuning fork arm sections 2a, 2b and the detection tuning fork arm sections 3a, 3b are respectively constructed with a metallic member having a generally rectangular shape and disposed to be perpendicular to each other. Further, piezoelectric devices 7a, 7b are adhered through means such as an adhesive and solder to side surfaces of the driving tuning fork arm sections 2a, 2b, respectively. Still further, piezoelectric devices 8a, 8b are also adhered to side surfaces of the detection tuning fork arm sections 3a, 3b, respectively.
In addition to such a Watson type vibration gyro, there have been known a vibration gyro in which a tuning fork section is constructed integrally with a metal or piezoelectric material, exemplified by Japanese Unexamined Patent Publication Nos. 61-294361, 3-120415 and 5-267038. For convenience only, such a vibration gyro will here be referred to as an integral tuning fork type vibration gyro. FIG. 14 is an illustration of an example of such integral tuning fork type vibration gyros. In the integral tuning fork type vibration gyro, as shown in FIG. 14 an oscillator 11 is constructed using bar-like metallic members having a square cross section, and comprises two tuning fork arm sections 12a, 12b disposed in parallel to each other, a connecting section 14 integrally molded to make connection between one end portions of the tuning fork arm sections 12a, 12b, and a base (not shown) for fixing the connecting section 14. Further, driving piezoelectric devices 17a, 17b are adhered through means such as an adhesive and solder to outside surfaces of the tuning fork arm sections 12a, 12b, respectively. Still further, detection piezoelectric devices 18a, 18b are adhered to side surfaces of the tuning fork arm sections 12a, 12b perpendicular to the outside surfaces thereof, respectively.
In the case of such an integral tuning fork type vibration gyro, it is also possible that one tuning fork arm section serves for the driving only while the other tuning fork arm section acts for the detection only. In addition, as one modification of such an integral tuning fork type vibration gyro, there has also been known a vibration gyro in which the oscillator is made to have a generally H-like configuration.
However, the above-described prior tuning fork type vibration gyros create the following problems.
First, the Watson type vibration gyro has an extremely complicated structure, and in case that the driving tuning fork arm sections and the detection tuning fork arm sections have poor orthogonal accuracy and balance, the rotational angular velocity detection accuracy deteriorates. For this reason, it requires a high assembling accuracy, which does not lend itself to mass production. Particularly, in the case of mounting it in a movable body such as a motor vehicle and an industrial robot, because of the necessity of a shock resistance of several thousands G to several ten-thousands G, it is necessary to provide a cantilever between both arm sections so that the oscillator is supported through the cantilever, which results in a more complicated construction and in a lower mass production. In addition, since in the Watson type vibration gyro the oscillator has a three-dimensional structure and has a long tuning fork arm section, the sealing case becomes large in dimension, which leads to a vibration gyro having a large size as a whole.
On the other hand, the integral tuning fork type vibration gyro has a more simplified structure of the tuning fork sections as compared with the Watson type vibration gyro, while the leakage of vibration from the tuning fork sections to the external largely occurs. Accordingly, the supporting structure for the tuning fork sections needs a device to prevent such leakage, and therefore the configuration of the supporting section naturally results in enlargement and complication, which leads to the increase of the whole vibration gyro in dimension. In addition, in the case of the integral tuning fork type vibration gyro, it is necessary that the piezoelectric devices be adhered to the side surfaces of the respective tuning fork arm sections perpendicular to each other, which substantially restricts the manufacturing process. In addition, it is necessary that electrodes be formed to the side surfaces of the respective tuning fork arm sections perpendicular to each other, if tuning fork sections are made of piezoelectric material. Thus, the integral tuning fork type vibration gyro also deteriorates in mass production as well as the Watson type vibration gyro.
Moreover, in the case of the Watson type vibration gyro and the integral tuning fork type vibration gyro, when the piezoelectric devices chiefly made of a ceramic are attached through a resin adhesive to the tuning fork arm sections made of a metal, a difference in coefficient of thermal expansion among the piezoelectric devices, the tuning fork arm sections and the adhesive occurs, with the result that, if the atmosphere temperature varies, the vibrating position of the oscillator varies due to the difference in coefficient of thermal expansion among them so that a temperature drift appears in the detection signal of the vibration gyro.